AGP speed 2X,4x,8X: What it really means!

The number only refers to the transfer rate of the AGP bus, which is an
extension of the PCI bus. Yes, faster is better but it primarily aides
in reducing load time of the texture data to the video cards local
memory therefore frames per sec increase is negligible at best. 3D
Benchmark programs may show improved scores but that is due to the
reduced latency of the data getting to the card.
The reason the AGP bus was invented was increase performance with older
cards when Video RAM prices were high and they had 4MB~16MB. The idea
was to use some of the System RAM to store the data that the video card
couldn't hold then transfer that data to it directly with a minimum of
CPU usage. The aperture size setting was to define how much of the
system RAM could be used for this purpose. Modern cards with all their
RAM and processing power no longer benefit much if at all save the
transfer speed to reduce load times hence the switch to PCI-express.

Chris Madsen wrote:

The number only refers to the transfer rate of the AGP bus, which is an
extension of the PCI bus. Yes, faster is better but it primarily aides
in reducing load time of the texture data to the video cards local
memory therefore frames per sec increase is negligible at best. 3D
Benchmark programs may show improved scores but that is due to the
reduced latency of the data getting to the card.
The reason the AGP bus was invented was increase performance with older
cards when Video RAM prices were high and they had 4MB~16MB. The idea
was to use some of the System RAM to store the data that the video card
couldn't hold then transfer that data to it directly with a minimum of
CPU usage. The aperture size setting was to define how much of the
system RAM could be used for this purpose. Modern cards with all their
RAM and processing power no longer benefit much if at all save the
transfer speed to reduce load times hence the switch to PCI-express.

PCI Express is considerably faster than AGP. The switch is mostly about
marketing.

--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net)

"Chris Madsen" wrote in message
...
The number only refers to the transfer rate of the AGP bus, which is an
extension of the PCI bus.

You neglect to say that AGP is 64bits wide and runs at 133MHz (at 1X),
compared to 32bits and 33MHz for PCI. So even AGP 1X is 8 times faster than
PCI. People might be confused into thinking that AGP 8X is only 8 times
faster than PCI. This is not true: it is 64 times faster.

Yes, faster is better but it primarily aides
in reducing load time of the texture data to the video cards local
memory therefore frames per sec increase is negligible at best.

[snip]

Modern cards with all their
RAM and processing power no longer benefit much if at all save the
transfer speed to reduce load times hence the switch to PCI-express.

I don't agree here. The performance of PCI-express is not dramatically
better than AGP 8X. And since the performance increase you see when going
from AGP 4x to AGP 8x is very very small, expect a similarly pathetic
performance boost moving to PCI-express. Its principle advantages are for
Raid disk controllers and the like, because the old PCI standard has become
a real bottleneck; AGP has not.

With respect to graphics controllers, the only real advantages PCI-Express
offers are that (A) it is bi-directional. This is beneficial in some CAD
type modelling environments. and (B) the PCI-Express connector standard can
carry more current than the PCI connector. Bottom line is PCI-express is a
complete waste of time for gaming speed improvements. Anyone looking to
"upgrade" their graphics card specifically to take advantage of PCI-Express
is going to be very disappointed.

Chip

You neglect to say that AGP is 64bits wide and runs at 133MHz (at 1X),
compared to 32bits and 33MHz for PCI. So even AGP 1X is 8 times

AGP runs at 66Mhz at 1X not 133Mhz. 133Mhz is 2X

"PRIVATE1964" wrote in message
...
You neglect to say that AGP is 64bits wide and runs at 133MHz (at 1X),
compared to 32bits and 33MHz for PCI. So even AGP 1X is 8 times

AGP runs at 66Mhz at 1X not 133Mhz. 133Mhz is 2X

Of course it does. What on earth was I thinking of. Doh!

Chip

Chip wrote:

The performance of PCI-express is not dramatically
better than AGP 8X. And since the performance increase you see when going
from AGP 4x to AGP 8x is very very small, expect a similarly pathetic
performance boost moving to PCI-express. Its principle advantages are for
Raid disk controllers and the like, because the old PCI standard has become
a real bottleneck; AGP has not.
{snip}
With respect to graphics controllers, the only real advantages PCI-Express
offers are that (A) it is bi-directional. This is beneficial in some CAD
type modelling environments. and (B) the PCI-Express connector standard can
carry more current than the PCI connector. Bottom line is PCI-express is a
complete waste of time for gaming speed improvements. Anyone looking to
"upgrade" their graphics card specifically to take advantage of PCI-Express
is going to be very disappointed.

I'm not sure about the CAD application benefits but the old PCI bus is
still fast enough for RAID as its capacity is 133MB/s and the best RAID
speed will only burst at ~85MB/s in real world. Another big difference
is that PCI-express is a "serial" connection not "parallel" like AGP or
standard PCI and serial devices can invariably be clocked much higher
for better throughput. Power shouldn't be much of an issue as most
hungry cards have connectors on them to get what they need directly from
the main supply anyway.

Chris

With respect to graphics controllers, the only real advantages
PCI-Express offers are that (A) it is bi-directional. This is
beneficial in some CAD type modelling environments. and (B) the

The other advantage to PCI express is having multiple slots. It always
irked me that if I upgraded my AGP card, I couldn't run both at the same
time. Now if your current card is slow with new games, but has great VIVO
features, you won't need to look for another card that also does VIVO when
shopping for a new card.

Of course it does. What on earth was I thinking of. Doh!


It happens to the best of us, but I have to admit very rarely with myself do I
slip up. ; )

"serial" connection not "parallel"

I really don't understand that concept. How can data be faster moving down a
single path? Is it because the path can be run at a much higher clock speed?
What happens with parrallel does the data get corrupted easier?

PRIVATE1964 wrote:
"serial" connection not "parallel"


I really don't understand that concept. How can data be faster moving down a
single path? Is it because the path can be run at a much higher clock speed?
What happens with parrallel does the data get corrupted easier?

The speed difference between serial and parallel is; a byte needs to be
converted twice as often when its transmitted in parallel than when its
done serially. The main reason most things are done in parallel is
because its more cost effective and is easier to implement. Serial data
paths can't be too long because of resistance of the conductor which
causes data loss, thats why they use multiple shorter paths instead. The
main problem comes when there is too many of those shorter paths close
together and have "cross-talk" which causes data corruption. If any data
is lost or corrupt it needs to be re-sent and reduces throughput. This
happens more often with a parallel connection than serial, thats why
they needed the 80 conductor cables for IDE to support higher
throughput. Every other conductor is tied to ground to reduce cross-talk
between adjacent data lines. Hope this clears things up a bit.

Chris